This invention relates to a method for developing electrostatic latent images formed on an electrostatic image-bearing member, particularly to a method for development by forming a thin and uniform toner layer on a toner carrying member.
In the prior art, the following methods have been known as methods for carrying out development by use of a substantially non-magnetic one-component toner, i.e., a non-magnetic or weakly magnetic toner.
For example, there is known a method for developing electrostatic images comprising causing a developer-carrying member carrying a developer on the surface thereof to face a latent image-bearing member, and developing a latent image on the latent image-bearing member, wherein the developer accumulated in a developer-storing means below the developer-carrying member is drawn up onto the developer carrying member while giving vibration to the developer only at the drawing-up position to activate the developer and caused to form a developer layer to a desired thickness on the developer carrying member, which developer layer is then supplied for development.
Another method comprises providing a rotatable magnetic roller for forming a magnetic brush by attracting magnetic carriers for charging one-component toner particles and a developing roller for developing electrostatic latent images on an electrostatic latent image-bearing member by transfer of the toner particles onto the roller, and developing the electrostatic images, while maintaining a gap between the electrostatic image-bearing member and the developing roller at the developing station, with the gap being set greater than the thickness of the coated toner layer on the developing roller.
Still another method comprises providing a movable developer-carrying means which carries, conveys and feeds a developer to a latent image (electrostatic image)-bearing member, a developer-feeding means and a movable coating means which receives feed of the developer from the developer-means and applies the developer to the above movable developer-carrying means, said movable coating means having a fiber brush for carrying the developer on its surface and contacting the above movable developer-carrying means to apply the toner uniformly to the above movable developer-carrying means at the contacted portion, while moving at higher speed in the same direction as the movable developer-carrying means than the movable developer-carrying means, and approaching the coated layer to the electrostatic latent image portion.
In these methods, compared with a conventional developing method using a one-component toner, a stronger force is applied when a toner is applied onto a toner carrying member, whereby the triboelectric charge imparted to the toner is liable to become higher and to increase with the continuation of developing operation. Thus, a difficulty is encountered that the image density of the resultant copies varies with the elapse of time and the quality of the copies cannot be maintained constant.
Furthermore, in these methods, a substantially non-magnetic insulating toner is carried on a carrying member at the developing station mainly through a non-magnetic force and used for development. Thus, the force for carrying the toner on the toner carrying member around the developing station consists predominantly of an electrostatic attracting force and a physical attaching force and, in this respect, several difficulties are encountered when compared with a conventional developing method using an insulating magnetic toner where the toner is carried on a carrying member through a magnetic force, an electrostatic force, etc. For example, most toners cannot be applied onto the carrying member to form a relatively thin uniform layer. Further, even if relatively uniformly applied, a phenomenon of so-called fogging occurs where the toner is attached to non-image portions. Further, even if applied to form a thin and uniform layer, the amount of toner attached onto image portions is insufficient to result in images of low densities. Moreover, most toners can produce poor images of low fidelity and low resolution. Most toners can cause decrease in image density or a low quality of image on repeated use. Furthermore, most toners are accompanied with such defects as decrease in image density at one time and fogging at another time, when encountered with changes in environmental conditions including high temperature and high humidity conditions and low temperature and low humidity conditions.
On the other hand, the developing method using a one-component magnetic developer is not only expensive but also is encountered with difficulty in giving beautiful chromatic images, because a large proportion of magnetic material is contained in the magnetic toner particles, compared with non-magnetic or weakly magnetic toner particles.